The studies conducted in conjunction with this grant deal largely with the properties of a peroxidase in rat uterine fluid, human cervical mucus and eosinophils, with particular regard to its toxic effect on bacteria, fungi, viruses and spermatozoa when combined with H2O2 and an appropriate oxidizable cofactor such as iodide, bromide or thiocyanate ions. The uterine peroxidase may be either leukocytic in origin (eosinophil, neutrophil) or it may be secreted by epithelial cells lining the cavity. Such a system may exert a considerable influence on the control of the microbial flora in the vaginal and cervical canal and on the control of sperm motility and thus fertilization. Abnormalities in this system will be sought in patients with vaginal or cervical infection or with infertility problems.